This invention relates to a metering system for corrosive liquids. Particularly, this invention relates to an automatic metering system for corrosive liquids useful in metal strip pickling operations.
In the production of metal alloys of various compositions which are fabricated into various forms, including plate, sheet and strip products, it is known to use pickling operations during various stages of the fabrication. The purpose for such pickling operations is to clean any oil, scale and other contaminants from the surface of the metal before further processing or before shipment. Typically, pickling operations include the use of harsh, caustic and corrosive liquids, such as nitric, sulfuric and hydrofluoric acids, halogenated solvents and boiling caustics. Such corrosive liquids are also extremely corrosive to equipment handling such liquids and as a result, special equipment is necessary.
Generally, there are three known ways in the art for metering corrosive liquids, such as hydrofluoric acid, in metal strip pickling operations. One known method includes metering of the corrosive liquids by timing flow from a pipe to the pickling tanks. A second known method includes using an auxiliary tank which is calibrated for small volumes of acid. A third method is by weighing the caustic liquid to be used in the operation. While such methods have been useful for metering corrosive liquids, they are not without problems. Such methods are inadequate, for none of them provide the accuracy required when making frequent additions to a pickling operation, for example. Furthermore, none of these methods provide repeatedly accurate measurements.
What is needed, then, is a metering system for automatically controlling and monitoring corrosive liquids. The system should provide repeatable and accurate measurements, and should be suitable for automatically metering the desired volume of corrosive liquids. The system should also be suitable for incorporation into any automated pickling operation, such as for strip products.